1. Field of the Invention
The present invention relates to systems for feeding solutions to patients. More particularly, the present invention relates to a feeding set adaptor which is used in association with a medical solution pump. The pump and an infusion set which is acted on by the pump typically form a system for the monitoring of fluid pressures, for bubble detection and for selective flow occlusion of solutions being fed to a patient. Specifically, the invention relates to an adaptor which is used to connect various parts of an infusion set and to integrate them with the pump to enable the monitoring of fluid pressures, the detection of bubbles, and the selective occlusion of fluid flow to prevent freeflow conditions.
2. State of the Art
There are numerous situations in which a solution must be fed to a patient over a period of time. In some situations, the solution is provided directly into the blood stream of the patient. Saline solutions and medications supplied in such a manner are typically referred to as parenteral solutions.
In contrast to a parenteral system, an enteral feeding system is used to provide nutrient solutions to patients who, for one reason or another, are unable to eat for themselves. Such a system typically includes a pump which is attached to an input tube connected to a supply container and to an output tube which is connected to a patient. The pump draws nutrient solution from the supply container and delivers the solution to the patient. By adjusting the number of rotations of the motor, or the frequency of rotations, in the pump, an enteral feeding pump can adjust its output to deliver a predetermined amount of nutrient solution (or even medication) at a desired rate.
A significant problem with many currently available enteral feeding systems, is that the intake and output tubes may become occluded. Unlike parenteral solutions, enteral feeding solutions have a relatively high viscosity, as they must carry sufficient nutrition to sustain the patient. Occlusion can occur, for example, if a fibrous substance is included in the enteral feeding solution and somehow combines to interfere with flow through the tube. Occlusion can also occur if a tube is bent sufficiently to interfere with flow therethrough, or if a roller clamp (as is commonly used for intravenous applications) is not sufficiently opened. Because of the viscosity of the solution, the amount of kinking of the tube or other interference required to interfere with solution flow is significantly less than that required in a parenteral infusion set.
If the intake tube becomes occluded, insufficient solution may be supplied to the pump, and thus to the patient. If the output tube becomes occluded, the flow of solution may be blocked, or the solution may be delivered suddenly at unusually high pressures. Additionally, medical personnel may fail to notice that the supply container is out of solution, or may not properly mount the intake and/or output tubes in the pump, thereby preventing the proper amount of solution from being delivered to the patient. Any of these scenarios can have tragic consequences if allowed to continue for a prolonged period of time.
Yet another concern with enteral feeding systems is that of viscosity of the solution and viscosity changes as a container full of solution is pumped to a patient. Knowing the viscosity of the fluid being pumped through the enteral feeding system is important because different viscosities are pumped at different rates by the enteral feeding pump. For example, a lower quantity of a highly viscous solution will be pumped by a given number of rotations of the enteral feeding pump motor than will be moved by the same pump when the solution has low viscosity. In other words, the amount of solution fed to the patient can differ substantially depending on the solution's viscosity. Thus, unless the pump is able to accurately determine and compensate for viscosity changes in the solution (i.e. by increasing or decreasing the rotations of the pump rotor in a given period of time), it is difficult to know exactly how much of the solution has been fed to the patient.
Yet another problem which is of concern during the administration of enteral feeding solutions is the presence of air bubbles. While very small air bubbles will not cause harm, large bubbles entering the blood stream can cause serious medical complications and even death. Thus, it is important to monitor the solution to ensure that any bubbles present do not exceed the desired threshold.
Still another problem which is present in enteral feeding systems, and the like, is freeflow. Often, the infusion set is placed in a free standing arrangement in which gravity forces the solution into the patient. The rate at which the solution enters the patient can be roughly controlled by various clamps, such as roller clamps, which are currently available on the market.
In many applications, it is necessary to precisely control the amount of solution which enters the patient. When this is the case, a regulating device, such as an enteral feeding pump, is placed along the infusion set to control the rate at which the solution is fed to the patient. In applications where a pump, etc., is used, the clamps used to regulate flow are typically opened to their fullest extent to prevent the clamp from interfering with the proper functioning of the pump. The clamp is opened with the expectation that the enteral feeding pump will control fluid flow through the infusion set.
It is not uncommon, for emergencies or other distractions to prevent the medical personnel from properly loading the infusion set in the enteral feeding pump. When the infusion set is not properly loaded in the pump and the clamp has been opened, a situation known as freeflow often develops. The force of gravity causes the solution to flow freely into the patient unchecked by the pump or other regulating device. Under a freeflow condition, an amount of solution many times the desired dose can be supplied to the patient within a relatively short time period. This can be particularly dangerous if the solution contains potent medicines and/or the patient's body is not physically strong enough to adjust to the large inflow of solution.
Numerous devices have been developed in an attempt to prevent free flow conditions. Such devices, however, typically add significantly to the overall cost of the infusion set and some provide only marginal protection against free flow. Thus, there is a need for a device that prevents a freeflow condition while allowing controlled flow through the infusion set. There is also a need for such a device which prevents freeflow if an infusion set is not properly mounted in a pump or other regulating means. Furthermore, there is a need for a device which prevents freeflow and which is inexpensive and easy to use.
The fluid flow monitoring mechanism disclosed in U.S. Pat. No. 5,720,721 and the anti-freeflow mechanism described in U.S. Pat. No. 5,704,584 (both of which are expressly incorporated herein) provided a significant improvement in monitoring for enteral feeding pumps and in control of freeflow situations.
As shown in FIG. 1A, the pump taught in U.S. Pat. No. 5,720,721 uses two pressure sensors to monitor viscosity and occlusions, and to enable the enteral feeding pump to compensate for the varying amount of solution which will pass through the pump with each rotation of the rotor. The pressure sensors engage the elastic tube of the infusion set and monitor changes in the strain on the infusion set by occlusions and viscosity changes. The strain information can then be processed by the pump and adjustments made to the number of rotations of the pump rotor to compensate. In the event that the occlusion is too severe to compensate by modification of the rotor rotations, the pump is shut down and an alarm signal generated so that replacement tubing may be provided.
Also included was an air detector which was disposed in the pump. The air detector was disposed in communication with the pump and used ultrasonic energy to determine if bubbles were present in the conduit.
While the pressure sensor system of U.S. Pat. No. 5,720,721 is a significant improvement over the art, it does have limitations. The pressure sensors described in the '721 patent are relatively expensive and must be properly mounted in the pump. Additionally, the person loading the pump must make sure that the upstream and downstream portions of the infusion set are properly loaded in the pump housing so that they engage the pressure sensors in the proper manner. Failure to properly load the infusion set can interfere with the functioning of the pressure sensors. In particular, if the clinician overly stretches the tubing as he or she wraps it around the pump, the tube on one side of the pump rotor will be stretched to a greater degree than the opposing side. This, in turn, can effect pump accuracy if too severe.
One manner for decreasing the costs of pressure sensors is to use an optical sensors. While there are several methods for using optical sensors to determine the presence of occlusions, each has significant drawbacks. Some methods only allow the mechanism to determine when the pressure exceeds a certain threshold. This is done by detecting when the expanding tube of the infusion set engages a surface, thereby modifying reflection or refraction of light. Other methods require complex calculations of refraction indexes or otherwise provide relatively limited information on small pressure changes. Additionally, some methods can vary based on the material from which the infusion set is formed, or based on whether the tube of the infusion set is opaque or transparent.
In addition to the above, many mechanisms for monitoring pressure within an infusion set lack an inherent failure detector. For example, if a sensor is configured to sense only when the expanding infusion set tube engages a transparent surface, the failure to record a reflected signal may mean that the tube has not expanded. In certain situations, however, the lack of reflected signal could also mean that the sensor has failed and is either not sending the signal or is not receiving the reflected signal.
In addition to the concerns with pressure sensing technology of the prior pumps, the pumps also used ultrasonic technology for bubble detection. While this technology is highly accurate, it is also expensive. An ultrasonic sensor can cost as much as 50 times as much as an optical sensor.
In addition to the above, the anti-freeflow technology discussed in U.S. Pat. No. 5,704,584 has limitations. While the occluder mechanism works well, it is relatively expensive to form a separate mechanism to selectively stop flow through the infusion set. A separate pinch clip occludes such as that shown in FIG. 1B can add fifteen to twenty percent to the cost of an infusion set. While the cost per unit is rather small, daily replacement of the infusion set can add up to significant costs. In a highly competitive medical environment, even a few cents per unit can dramatically effect sales quantities.
Thus, there is a need for a mechanism which can enable improved pressure monitoring, improved air detection and improved flow occlusion. Such a mechanism should be relatively inexpensive and should lessen the likelihood of errors in use of the pump and infusion set. Furthermore, it should enable the use of infusion sets made from a variety of materials.